Sheet Metal Workers' Local #18 covers the entire state of Wisconsin with the exception of Ashland, Bayfield, Douglas and Iron counties.

Local #18 was established October 1, 1982, as a result of an amalgamation of former locals 24 (Milwaukee), 33 (Fox Valley), 35 (Racine/Kenosha/Walworth), 42 (Fond du Lac/Manitowoc/Sheboygan), 64 (Eau Claire/La Crosse/Wausau), 279 (Madison), and 416 (Janesville).